Cerebral blood flow and glucose metabolism in hypothyroidism: A positron emission tomography study

Hypothyroidism is often associated with defective memory, psychomotor slowi ng, and depression. However, the relationship between thyroid status and co gnitive or psychiatric disturbances remains unclear. Using psychometric sca les, 10 patients who had undergone total thyroidectomy for thyroid carcinom a were evaluated for depression, anxiety, and psychomotor slowing; they wer e examined both when euthyroid and hypothyroid after thyroid hormone withdr awal. Positron emission tomography was used, with oxygen-15-labeled water a nd fluorine-18F-labeled 2-deoxy-2fluoro-D-glucose as the tracers, to correl ate the regional cerebral blood flow and cerebral glucose metabolism with t he mental state in patients. Two different image analysis techniques (regio ns of interest and statistical parametric maps) were applied. In hypothyroi dism, there was a generalized decrease in regional cerebral blood flow (23. 4%, P < 0.001) and in cerebral glucose metabolism (12.1%, P < 0.001) and th ere were no specific local defects. Patients were also significantly more d epressed (P < 0.001), anxious (P < 0.001) and psychomotor slowed (P < 0.005 ) in hypo than in euthyroid status. These results indicate that the brain a ctivity was globally reduced in severe hypothyroidism of short duration wit hout the regional modifications usually observed in primary depression.